Quote:
Originally Posted by orange
I have no idea what you really mean. The plane's momentum is 0.
p = mv
The plane has no velocity. We start up the engines, energy drives the plane forward. It tries to move forward but it is in contact with the ground. The contact points are the wheels. Friction at the points of contact (i.e. where the rubber meets the road) resists any forward motion of the plane, basically pushing back. Since the contact points can't move forward the wheels spin so a new bit of wheel now contacts a new bit of road.
On the conveyor belt, the "road" also spins like the wheels. The new bit of road is in the same place as the first bit of road. There are now new contact points between new bits of wheel and new bits of road, but the position of these points relative to the surrounding ground is the same as the original position. The plane has not moved relative to the surrounding ground - and more importantly air. The plane's velocity remains 0. The plane's momentum remains 0. The energy that was spent spun the wheels and the conveyor belt.
Rinse and repeat.
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that's what i thought at first, too. but the first step in all of this is that the engines turn on. there's now a force that has to be counteracted, and the conveyor will try move to keep the plane in the same spot.
I get that. when the conveyor tries to do this it causes the wheel to spin faster. but because how fast the wheel spins has no effect on the speed of the plane, it doesn't matter.